img tags that create Share and Save icons throw errors

W3C Markup Validator gives me 5 similar error messages for the tags that create the Facebook Share icon, the Twitter “Tweet” icon, and the Pinterest “Save” icon.
They indicate that width=’auto’ and height=’auto’ are not allowed, but must have numerical values.
I found, in a plugin file, the snippets of code that create the tags in the source code but they cannot be edited there. How can I correct these errors?
Thank you.